This application relates to the hard facing of surfaces and to the weld rod used in such hard facing, and, more particularly, to hard facing rock bits with tungsten carbide/cobalt material.
A rock bit is a specialized drill bit used in the drilling of oil and gas wells. A conventional rock bit has three rotatable, conical cutters with teeth thereon. The conical cutters are mounted in a generally triangular arrangement so as to protrude from the lower end of a housing termed an arm. The rock bit is attached to the lower end of a drill string of hollow tubes, and a lubricant termed "mud" is pumped through the drill string to lubricate the rock bit and/or wash rock cuttings away from the rock bit during the drilling operation.
The rock bit is made of a strong, ductile steel selected to have good strength and toughness. This steel cannot itself serve as the cutting face of the conical cutters, because it would be rapidly worn away by the abrasive contact with the rock being cut. Instead, it has long been the practice to place a hard coating, usually termed a "hard facing", on the teeth and other surfaces of the rock bit, termed the "substrate", that are subjected to the greatest intensity of wear during the cutting operation. The hard facing resists wear, so that the rock bit enjoys the benefits of both the tough steel body and the wear resistant coating.
The hard facing material is usually a mixture of a hard, wear resistant material embedded in a metallic matrix. The metallic matrix is fused with the surface of the steel in the rock bit by welding, to ensure adherence of the coating to the substrate. The wear-resistant material is typically tungsten carbide particles mixed with cobalt. The wear-resistant material is placed into a steel tube, which serves as a weld rod during weld application of the hard facing to the rock bit surface.
The tungsten carbide/cobalt hard facing approach has proved highly successful in extending the service lives of rock bits, and is widely used commercially. However, there is always a need for an improved approach that achieves improved rock bit performance with decreased wear and increased operating life. The present invention fulfills this need, and further provides related advantages.